You can set your own difficulty by adding a / or + to your address. But I never understood it. Also if you use a local one, don't use an address as your username. Just u and p.
And when using public, don't choose a password, just use p.
And when using public, don't choose a password, just use p.
On a local p2pool node uou can use any username you want. If you have several miners, use a different one for each of them to keep track of how they behave.
However, when configuring the p2pool node you should always use an address of a secure wallet with the "-a" parameter. If you don't p2pool uses an address genereated by the bitcoind it connects to and you shouldn't do that: the address is on a wallet exposed to the Internet: any security breach and your wallet is gone.
There are two difficulties you can setup and usually you don't need to.
The first one is the share difficulty used to compute your rewards, the minimum is enforced by the p2pool network and can't be set (you can see it in logs and on the p2pool web interface). The only reason to raise it is if you have a sizeable portion of the p2pool hashrate and would like to leave room for smaller miners in the sharechain (its size is bounded), this shouldn't be needed in latest p2pool: IIRC the rate of share submission is automatically adjusted now.
If for any reason you should want to change it, you can simply append the difficulty after a "/". If your username is "foo" and wanted difficulty is 20000, just use "foo/20000".
The second one is the miner's target difficulty, used to compute the estimated hashrate in p2pool. It's adjusted automatically so that the rate of shares submitted is ~1 every second which both gives accurate hashrate estimations and low load on p2pool. If you want to change it, you use "+" instead of "/": "foo+64". You can combine the two: "foo/20000+64".
TL;DR: don't use difficulty parameters in the username, you most probably don't need them.
However, since the mining difficulty you use makes no difference to the number of share chain shares you get, as long at it is less than the share chain difficulty, it really doesn't matter.
What does matter, is how much work you get cgminer, p2pool and the network to do.
For 72GH/s I was using +64 ... I like powers of 2
My setting was to get a share every few seconds and thus not have a screen full of crap scrolling by, 64 gave me a share every ~4s and also ensures that the difficulty wasn't swapping and changing.
Aside: with normal pool mining I use 256 diff (and have even since I was above 2GH/s many many months ago)
